The prior art recognizes the benefits of having cruciform style recess drive systems. Exemplary issued patents that describe various alternatives include:
U.S. Pat. No. 2,046,839, entitled SCREW by Phillips, et al (relating to the well known Phillips head screws)
U.S. Pat. No. 2,592,462, entitled RECESSED HEAD FASTENER by Phippard**
U.K. Patent No. 1,006,509, entitled IMPROVEMENTS IN OR RELATING TO SCREW THREADED FASTENERS AND DRIVERS FOR USE THEREWITH, by GKN Screws and Fasteners, Ltd. (the so called POZIDRIV recess)**
U.K. Patent No. 1,521,141, entitled THREADED FASTENER by GKN Fasteners Ltd. (the so called SUPARIV recess)
U.S. Pat. No. 4,464,957, entitled FASTENER AND DRIVER COMBINATION, by Gill**
Each of these listed patents, in its own way provides an understanding of the need to minimize the adverse effect of driver/recess separation when screws are being driven to affect an assembly. As will be appreciated by those skilled in the art, this phenomena is known by the term ‘cam-out’.
There is further given recognition that the cruciform systems and in association, a 3-wing system, where there are provided radial grooves as a means for driving the screw, have a need to provide for variations between the outer cone angle of the driver and the cone angle of the recess wings and that the driver cone angle 6 needs to be greater than the recess cone angle 5 and to encourage driver contact to occur at the top, outer face/edge, of the driving system 7 as seen in prior art FIG. 1. This is said to provide the best allowable contact for driving the screw and will aid toward minimizing cam-out and further reduce the effect of damage that might occur to the recess from a phenomena known as ‘spinning’. The cruciform drive systems further recognize the need for clearances between the recess wings and the driver wings for engagement between driver and recess to take place as shown in prior art FIG. 2. These clearances indicate that when driving torque is applied, clearances 104 will allow relative movement, between driver and recess, such that forces will only be applied through points 105.
In addition, the patents marked with an asterisk (**) recognize the need for a form of mechanical adhesion, between the recess and the driver such that placement of the screw, to an assembly, is made easier. This being achieved by a ‘wedging’ action when the driver and recess are initially engaged as illustrated in prior art FIG. 3. This wedging action is considered to take place at the bottom of the recess 107 and is also said to be an aid toward resisting cam-out.
In accordance with Gill, UK Patent No. 1,521,141, the clearances between recess and driver wings, are used to effect by allowing the axis of the driver and the axis of the recess to be misaligned such that one of the wings has the driver cone angle approaching closer to being parallel with the screw axis and further enhances the system in respect of minimizing cam-out.